The defendant also is charged with first-degree assault with a firearm and two counts of second-degree assault.

Watters, 42, pleaded not guilty on Thursday. He remained in the Snohomish County Jail, pending his October trial.

Watters reportedly became entangled in a beef over a $20 marijuana deal among a group of young people.

The two groups agreed to meet up that night at Blue Stilly to settle their dispute, according to witnesses. Both sides called for backup, recruiting friends. One girl reportedly called her father, complaining that she’d been assaulted by Mumm’s friend.

That man reportedly called Watters to help him confront the guys who hit his daughter, court papers said. The man confirmed that Watters would be carrying a gun.

A witness told police that’s when Mumm got out of a BMW at the park he pointed a gun at the rival driver. A witness said Mumm fired the gun in the air.

Meanwhile, Watters arrived in his pickup. Detectives were told that after Mumm fired his gun, a shootout happened between him and Watters. A witness also told police that he saw Watters ram his pickup into the BMW on Highway 530 and shoot at the vehicle.

Mumm’s friend eventually parked at a gas station. That’s where sheriff’s deputies found the injured man. Mumm was motionless in the passenger seat with an obvious gunshot wound to the head. He was rushed to the hospital, but died the next day.

Detectives later reviewed surveillance video from the gas station and saw the slain man’s friend hide something. The man eventually told police he’d hidden Mumm’s gun.

Investigators spoke with Watters, who reportedly admitted that he fired at Mumm, court papers said.

He said his pickup came face-to-face with a BMW and he saw the passenger point a gun at him through the windshield. He held up both hands while the BMW backed up. He said the passenger held a gun out the window and fired it into the air. He said as the car drove around his pickup, the passenger shot at him. That’s when he grabbed his gun, loaded it and returned fire, court papers said. Watters said he fired three rounds and believed he’d struck the passenger in the shoulder.

He also reportedly admitted that he chased after the BMW and tried to bump it off the road, court papers said.

“The defendant joined a fight in which he had no direct involvement and brought a gun,” Twitchell wrote. “Then he shot and killed Ryan Mumm. After shooting Mumm, the defendant chased the car Mumm was in; rammed it; and continued shooting at it.”

Watters has no prior felony convictions. He faces decades behind bars if he is convicted.